The invention relates to a drive for closure elements, in particular garage and industrial doors, and for example also for roller shutters, with a reference value generator arranged in the motor or in the gearing of the drive for determining the actual position of the closure element.
Such a drive is already known from DE 38 01 245 C in the form of a door drive. The door drive disclosed there comprises a generator disc, which is connected so as to be co-rotating with a part of the drive motor arranged rotating and to which a scanning device is assigned, by means of which the rotary motion of the generator disc is converted into a corresponding number of pulses. The number of pulses is detected by a counting device, the counter status of which corresponds to a prescribed position of the door. The arrangement also comprises a reference point indicator device, which for example consists of at least a switch fixed to the door frame and an actuator fixed to the door leaf, by means of which the switch is actuated when the door passes by the corresponding position of the frame. When the switch is actuated, a synchronising signal is generated which forces the counter device to set a certain value, for example the input value of zero. The door is stopped when a comparison adjustment detects agreement between the counter value and a setpoint value corresponding to the desired position of the door. As an alternative to a switch fixed to the door frame as a reference point indicator device, the motion of the door can also be reproduced onto a reference point indicator device by means of step-down gearing. The reproduction of the door motion by means of step-down gearing, however, can lead to a comparatively less exact resolution of the motion sequence.